• Journal of Korean Biological Nursing Science
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• v.18 no.1
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• pp.9-16
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• 2016

Purpose: The purpose of this exploratory study was to find a specific time of day with a stable cortisol level and to investigate the relationship between salivary cortisol and sleep. Methods: A total of 36 Korean female college students participated in the study. Salivary specimens were collected 6 times a day for 2 days in different stressful situations. Sleep characteristics were measured using an actigraph while salivary specimens were collected. Perceived stress was evaluated using the Global Assessment of Recent Stress. Results: Depending on whether there were morning peak and/or afternoon elevations in the cortisol levels, the type of diurnal cortisol pattern was classified into 4 types. None of the cortisol levels in different times of the day showed significant relationships to perceived stress levels. Cortisol levels in the morning, levels of peak cortisol and diurnal differences of cortisol were significantly correlated with sleep duration. The time with most stable cortisol level was 9-10 pm. Conclusion: It is recommended that measurements of salivary cortisol are taken from 9-10 pm since it showed a stable value regardless of diurnal cortisol rhythm and sleep. Sleep duration should be considered as an important confounding factor in measuring cortisol levels in the morning and the diurnal differences of cortisol.

• Proceedings of the Zoological Society Korea Conference
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• 1999.10b
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• pp.178.2-178
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• 1999

No Abstract, See Full Text

• Sleep Medicine and Psychophysiology
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• v.21 no.2
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• pp.51-60
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• 2014

A 'circadian rhythm' is a self-sustained biological rhythm (cycle) that repeats itself approximately every 24 hours. Circadian rhythms are generated by an internal clock, or pacemaker, and persist even in the absence of environmental time cues, collectively termed 'zeitgebers.' Although organisms generate circadian rhythms internally, they are entrained by environmental stimuli, particularly the light-dark cycle. Measurement of the endogenous melatonin rhythm provides relatively reliable surrogate way of assessing the timing of the internal circadian clock. Also, core body temperature and cortisol can be used as markers of circadian rhythms. The sleep-wake cycle, body temperature, and melatonin rhythm have a stable internal phase relationship in humans and other diurnal species. They play an important role in controlling daily behavioral rhythms including task performance, blood pressure, and synthesis and secretion of several hormones. In this review, we address not only the properties, methods of measurement, and markers of circadian rhythms, but also the physiological and psychological importance of human circadian rhythms.

• Korean Journal of Occupational Health Nursing
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• v.18 no.1
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• pp.14-21
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• 2009

Purpose: This study was performed to investigate the effect of shift work on diurnal blood pressure (BP) pattern in nurses. Method: We studied 20 healthy nurses engaged in 3 shift work. 24-hour ambulatory BP monitoring was performed to each nurse two times during the day and night shift. Five nurses were excluded because of inadequate BP measurement. Results: All subjects were female. The mean age was 27.4 years (range: 23-33 years) and mean body mass index was 19.7 Kg/$m^2$ (range: 18.0-21.2 Kg/$m^2$). The changes of systolic BP ($17.8{\pm}9.1$ vs. $13.2{\pm}4.7%$, p=0.031), diastolic BP ($22.3{\pm}8.7$ vs. $17.3{\pm}9.0%$, p=0.061), and heart rate ($25.2{\pm}5.2$ vs. $12.5{\pm}8.7%$, p=0.001) during the sleeping period were decreased after a night shift compared with day shift. The non-dipper group significantly increased from 20% to 40% after a night shift (p=0.018). Conclusion: Working night shift is significantly associated with non-dipper status in nurses.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.9 no.1
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• pp.113-122
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• 2002

Purpose: The purpose of this study was to identify characteristics of serum ferrum, TIBC and ferritin's circadian rhythm in normal adults and to prepare a standard to determine the examination material extraction time. Method: Nine women and ten men made up the convenience sample for this study they were from the staff of D university hospital and students in D medical School located in K city who met the qualifications for inclusion in the sample. The value of serum ferrum, TIBC and circadian rhythm were calculated as follows : First. each variable's amplitude. the acrophase and average were measured for a 24 hour cycle using the cosinor method, and then each person's rhythm was analyzed. Results: There were significant serum iron circadian rhythm for both men and women (p<.05). For the men, mesor was $105.91{\mu}g/dl$. amplitude was $29.52{\mu}g/dl$, and the acrophase was 9.76 hour. For the women, mesor was $108.17{\mu}g/dl$, amplitude was $28.09{\mu}g/dl$, and the acrophase was 11.42 hour The rhythm change of TIBC was only significant for the women (p<.05), mesor was 383.39mg/dl, amplitude was 60.29mg/dl. and the acrophase was 14.93hour. As for the circadian rhythm of the ferritin, there are no diurnal variation in either sex, men were between 134.0ng/ml and 137.4ng/ml, and women, between 29.1ng/ml and 30.1ng/ml. Conclusion: To help diagnose the boundary line between normal or deficiency in iron, measurement should be carried out at a fixed time in the morning and evening, or a more proper time would be in the afternoon at the time when the width of amplitude is the least.

• Animal cells and systems
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• v.6 no.4
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• pp.293-299
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• 2002

We investigated seasonal variation of diurnal activity patterns in Jeiu ponies (Equus caballus). The data were collected from a semi-natural herd during daylight hours from March to September 1998. Over all months the mean proportion of time spent grazing was 83.7% ( $\pm$29.7 S.D.): that resting was 15.7$\pm$17%, grooming 0.7$\pm$1.2%, and moving 0.56$\pm$5.4%, Activity patterns varied with the seasons. The mean proportion of grazing mares peaked during late winter and early spring (March), when there was not enough food, and declined during other seasons (between May and September), when food was abundant. The mean proportion of mares that were resting and mutual grooming peaked in spring (April and May), at which time the weather was warm and food became abundant. During other seasons when grasses started to grow and the weather was mildly cool, these activities were less common. The mean proportion of mares that were moving peaked in June, although it was a small proportion of the total activity. For those mares without foals, resting periods were longer in older mares than in younger mares, but for the mares with foals this pattern was not evident. From these data, we hypothesize that the dominance hierarchy of the mares effects the diurnal activity pattern.

• Asian-Australasian Journal of Animal Sciences
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• v.14 no.9
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• pp.1209-1215
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• 2001

We conducted this study to investigate 24 h leptin profiles and to ascertain whether leptin secretion occurs in a pulsatile manner in cattle. Plasma leptin concentrations were measured every 10 min for 24 h in five Holstein steers aged 10 months. Simultaneously, feeding behavior was recorded every 5 min during this experiment. In two of the five cattle, leptin showed diurnal rhythmicity, which could be described by a cosine, with peaks between 15:00 and 16:00 and nadirs at around midnight. Pulsatile leptin release was quantified by model-free Cluster analysis. Plasma leptin showed a pulsatile pattern in all cattle, with an average number of pulses at 15 peaks/24 h. The daily number of pulses was not related to total time spent eating, ruminating or chewing. However, when divided into six 4 h time intervals, time spent ruminating was positively related with pulse number (p=0.05) in cattle showing no diurnal plasma leptin variation. These results suggest that cattle may have unique diurnal variation and pulsatile patterns of plasma leptin, differing from those of monogastric animals.

• Proceedings of the Korean Society of Embryo Transfer Conference
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• 2006.10a
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• pp.60-61
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• 2006

• Sleep Medicine and Psychophysiology
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• v.23 no.1
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• pp.25-28
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• 2016

Objectives: The retinoid-related orphan receptor A (RORA) gene has been reported to have an impact on circadian rhythm regulation. In this study, we analyzed the relationship between the RORA gene polymorphism and diurnal preference in Korean young adults. Methods: A population of 504 young adults was included in the study. All subjects were given and completed a 13-item composite scale for morningness (CSM). The RORA gene rs11071547 single-nucleotide polymorphism (SNP) was genotyped by PCR-based methods. Results: CSM score was not associated with genotype or allele carrier status of the RORA rs11071547 SNP. Conclusion: This result indicates that the RORA rs11071547 SNP does not play a role in diurnal preference.

• Journal of Physiology & Pathology in Korean Medicine
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• v.25 no.2
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• pp.311-317
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• 2011

The goal of this study was to clarify effects of sleep restriction on a diurnal rhythm of salivary cortisol and DHEA levels in Korean adolescents.83 middle school students were recruited to participate in restricted sleep period group (less than 4h/day) or unrestricted sleep period group (from 6h/day to 7h/day). Both were 14 to 17 years old. They were instructed to keep the sleep-awakening schedule and sampling protocol. Saliva samples of cortisol and DHEA were collected at 8h, 12h, 16h and 20h. Salivary hormones were analysed with salivary cortisol(or DHEA) EIA kit according to a fixed assay protocol. Cortisol levels of restricted sleep period group and unrestricted sleep period group significantly decreased according to the sampling times. Cortisol levels of sleep restricted group was significantly higher than those of usual sleep group at all sampling times. At 8h, DHEA levels of both groups were significantly higher than those at 12h, 16h and 20h. However, DHEA levels of restricted sleep period group did not differ from those of unrestricted sleep period group at all sampling times.Cortisol and DHEA levels of both group showed the typical diurnal rhythm regardless of sleep status. Restricted sleep may increased cortisol release, not DHEA release, which indicated a changed HPA axis.